A strong need exists for a more secure and safe interior chain lock for the doors of apartments and homes to prevent forcible entry by intruders. Available chain locks commonly employ a keeper attached to the interior of the door frame by two small screws and a chain anchor similarly attached to the interior side of the door. With such a lock, after the door has been partially opened from the inside, an intruder can easily burst into the dwelling by giving the door a sound kick or an abrupt push with the shoulder. Such action will dislodge the small screws which anchor the device to the door and door frame.
Therefore, the object of this invention is to improve on the known prior art and to satisfy the existing need of the art by the provision of a truly secure and safe interior chain lock for doors sometimes referred to as a "night lock". In accomplishing this objective, the invention provides a sturdy housing for a spring-urged extensible and retractable chain means and an associated latch element. The housing is securely anchored to the door lock cylinder housing means, which housing means cannot be separated from the outside of the door by an intruder. Such a housing means is disclosed in U.S. Pat. No. 3,934,437, issued Jan. 27, 1976 to Crepinsek and also in the above-referenced copending application. In some cases, the chain housing and guideway means may be connected with another type of door lock or may be securely attached to the door interior away from the door lock and bolt means. The chain and chain latch housing is further securely anchored to the free edge of the door through which the door lock bolt normally projects and thus the housing is secured to the door at two right angular planes as well as to the door lock cylinder housing making it virtually impossible to dislodge the housing.
Similarly, a sturdy mounting bracket for a keeper housing which receives the extensible chain latch element is secured firmly to both the inner face and to the edge of the door frame which faces the free edge of the door. The keeper housing has a pivotal connection with the frame attached mounting bracket and the keeper within the housing is spring-urged toward an active position relative to the coacting chain latch element and is mounted on a reciprocatory panic release member or knob which is normally accessible at the inner side of the door but only when the door is closed. Thus, in a panic situation on the inside of the door, the occupant of the dwelling space can quickly release the chain lock. However, with the chain lock active and with the door partially open, the panic release member swings with the pivoted keeper housing into an inaccessible chamber of the door frame behind the frame attached mounting bracket, and in this position neither the intruder nor the occupant can release the chain lock. Upon completely closing the door, the occupant can again release the chain lock by operating the reciprocatory release member or knob, and the spring-urged chain and latch element will retract automatically into the housing and guideway. The device is very strong, compact, neat in appearance, and relatively economical to manufacture. Its use gives great security in situations where presently-available chain locks and the like are practically useless in resisting forcible entry after the door is cracked open by the occupant.
Other features and advantages of the invention will become apparent during the course of the following description.